Heat sensitive detector

ABSTRACT

A heat sensitive detector is disclosed which includes an electrically conductive body providing a probe with a thin wall metallic end closure having a thermistor held thereagainst at the center of the closure, the body if desired having a compensating thermistor therein for temperature variation compensation.

Q United States Patent 1 [111 3,754,201

Adams Aug. 21, 1973 [54] HEAT SENSITIVE DETECTOR 3,435,400 3/1969Beckman 338/28 r r 2,588,014 3/1952 Knodsen..... [75] Inventor: RobertB. Adams, Tredyffnn Town- 2,933,708 4/1960 Elliot et a1 Shlp, ChesterCounty, Pa. 2,716,686 8/1955 Ehret ass/2s x [73] Assignee: MooreProducts Co., Spring House,

Pa. a Primary Examiner-C. L. Albritton [22] filed: 1972 Attorney-ZacharyT. Wobensmith, 2nd [211 Appl. No.: 223,601

Related US. Application Data [63] Continuation-impart of Ser. No.618,472, Feb. 24, [57] ABSTRACT i967, abandoned, and acontinuation-in-part of Ser.

No. 790,408, Jan. 10, 1969, Pat. No. 3,640, A heat sensitive detector isdisclosed which includes an electrically conductive body providing aprobe with a 8" 338/28 33 3 2 thin wall metallic end closure having athermistor held 58] Fie'ld 28 thereagainst at the center of the closure,the body if de- 5 6 sired having a compensating thermistor therein fortemperature variation compensation.

[56] References Cited UNITED STATES PATENTS 3 Claims,'2 Drawing Figures3,356,980 12/1967 Roberts 338/28 /9 /a /0 l6 /5 29, /Z f/ 22,; 29 20 351 Z5 CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of my prior application for patent Ser. No.618,472, filed Feb. 24, 1967, now abandoned, and of my prior applicationfor patent for FLOW METER, filed Jan. 10, 1969 Ser. No. 790,408, nowU.S. Pat. No. 3,640,133.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to measuring apparatus and more particularly to a heatsensitive detector in contact with a fluid for measuring flow and othervariables.

2. Description of the Prior Art Sensing devices of various types haveheretofore been proposed for use in flow measurement.

The U.S. Pat. to Chanaud, No. 3,279,251 shows various sensors responsiveto a fluid parameter fluctuation, such as pressure, temperature orvelocity and providing a signal. Reference is made specifically to theuse of a hot film anemometer or a hot wire anemometer.

In my prior application for Flow Meter, filed Jan. 10, 1969, Ser. No.790,408, now U.S. Pat. No. 3,640,133, a flow meter is shown in which asignal is made available attendant upon fluid oscillation, and theapparatus of the present invention is particularly suited for use in butis not limited to such a meter.

SUMMARY OF THE INVENTION 'In accordance with the invention a heatsensitive detector is provided in contact with a fluid which includes ametallic body providing a probe having an end surface of a thin metallicclosure exposed to the liquid and a temperature sensitive electricalelement or sensing thermistor held in a positive engagement with theclosure, an electrical conductor extending from the thermistor, and thebody, through the end closure serving to provide the other conductor ofthe thermistor, and a temperature compensating thermistor can also beprovided within the probe body.

It is the principal object of the present invention to provide animproved heat sensitive probe in which the body of the probe has a thinmetallic end closure wall against which the process fluid is in contacton the exterior, and a thermistor is in contact on the interior for heatsensing and for electrical contact.

It is a further object of the invention to provide a heat sensitivedetector in which a sensing thermistor is supported in an improvedmanner with adequate protection of the thermistor from the action of theprocess fluid and with thermal isolation of the thermistor fromsurrounding heat sinks.

It is a further object of the present invention to provide a heatsensitive detector having a thin metallic wall portion for contact bythe process fluid on one face and for engagement of a thermistor on theother face and with a continuous force maintained between the thermistorand the wall portion.

It is a further object of the invention to provide a heat sensitivedetector which is simple in construction and reliable in its operation.

Other objects and advantageous features will be apparent from thedescription and claims.

BRIEF DESCRIPTION OF THE DRAWINGS The nature and characteristic featuresof the invention will be more readily understood from the followingdescription taken in connection with the accompanying drawings formingpart hereof, in which:

FIG. 1 is a central sectional view of measuring apparatus in accordancewith the invention, and

FIG. 2 is a transverse sectional view taken approximately on the line2-2 of FIG. 1.

It should, of course, be understood that the description and drawingsherein are illustrative merely and that various modifications andchanges can be made in the structure disclosed without departing fromthe spirit of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularlyto the drawings the measuring apparatus in accordance with the inventionpreferably includes a probe body 10, shown as generally cylindrical witha reduced end portion 11 having an annular groove 12 spaced from theend.

The interior of the body 10 has a plurality of longitudinally axiallyaligned portions including in succession a cylindrical portion 15, acylindrical portion 16 terminating at a shoulder 17, an internallythreaded portion 18 from which a cylindrical portion 19 extends to acylindrical portion 20 which portion 20 extends to the end face 21 ofthe body 10.

The end face 21 of the body 10 has a closure 22 in the form of a discsecured thereto as at 22a in any desired manner such as by welding.

The closure 22 is preferably of metal of a thickness of less than 0.003inches, to provide good heat conductivity therethrough to the fluidbeing sensed as well as a spring like action as explained below.Furthermore a thin closure 22 restricts the heat loss through theclosure piece 22 to the body 10. Any suitable metal may be employedresistant to corrosion and of adequate strength, stainless steel andnickel being satisfactory for some uses.

The closure 22 has secured to the center thereof a thermistor 23 whichserves as a sensing element. The thermistor 23 is preferably in the formof a disc or block having at least one flat face 24 for contact with theclosure 22, the flat face 24 being at the center of the inner face ofthe closure 22 and with substantial clearance therearound for thermalisolation.

Inorder to hold the thermistor face 24 in engagement with the closure 22for thermal conductivity and electrical conductivity it is preferred touse a conductive epoxy cement at 25 of an epoxy resin with a silverfiller.

The thermistor 23 has its opposite face secured to a backup ring 26,preferably by the use of a conductive cement at 27 and as previouslyreferred to.The ring 26 has a central opening 28 for a conductor 29 fromthe thermistor 23, and in which conductor 29 is secured at 29a, as bysolder. The ring 26 has a clearance space 30 therearound.

In order to position the thermistor 23 at the end of the body 10, apositioning plug 32 is preferably employed having a press fit in thecylindrical portion 20 and insulating washers 31 are preferablyinterposed between the plug 32 and the back-up ring 26. The plug 22 ispreferably forced inwardly to aid in maintaining contact between thethermistor 23 and the closure 22 and for this purpose is urged to aposition to displace the center of the closure 22 about 0.003 inchesoutwardly from its initial flat condition.

The interior space within the threaded portion 18 can be filled as at 34with a potting compound.

If desired, a compensating thermistor 40 can be provided within theinterior of the probe body 10, mounted on a positioning plug 42 so thatit is in electrical and thermal contact with the body 10.

The plug 42 can be carried in the cylindrical portion 16 and engagedtherein with a press fit. The thermistor 40 has a lead 44 connected toit through metallic washer 41 which with the lead 29 extend through ahermetic sealing disc 46 carried in an end groove 47 in the body 10.

The conductor 29 provides one electrical contact for the thermistor 23,the other contact being provided by the grounded body 10. The conductor29 is connected to a control device 50 of well known type for making asignal available through conductor 51 in response to electricalresistance changes of the thermistor 23. The thermistor 40 can beconnected into the control device 50 for introducing its compensatingeffect.

In use, an electric current passing through the thermistor 23 heats thethermistor 23 to a temperature above the fluid on the other side ofclosure 22, the heat generated being transmitted through the heatconductive adhesive coating 25 and the closure 22. The pulsations of thefluid passing over the outer face of the closure 22 have a coolingeffect on the thermistor 23 which is effective to provide a signal.

The relationship described between the thermistor 23, the heatconductive coating 25 and the closure 22 provides a good frequencyresponse to changes in the surrounding fluid, either of flow or oftemperature, as desired.

The force applied and maintained on the closure 22 by the thermistor 23and the structure in engagement therewith provides a good electricalcontact and good heat conductivity. It has been found by experience thatunless this engagement force is employed, electrical and thermal contactbecomes lost through the effect of aging, vibration and temperaturechange.

The thin metal of the closure 22 contributes to good heat conductivitywith respect to the thermistor 23 and a spring like action to maintainthe desired engage ment.

The mounting of the thermistor 23 at the center of the thin walledclosure 22 and the free peripheral portions of the closure 22 beyond thethermistor 23 provides thermal insulation from the surrounding heatsinks, including the body 10 and the structure in which it is carried.

The compensatory thermistor 40 located in the interior of the body 10can be utilized to compensate for temperature changes which occurgradually within the fluid.

A thermally insulating coating 35, such as teflon, may be applied to theoutside surface of closure 22 at all points except those directlyopposite thermistor 23 providing a window, as at 36, for the purpose ofconcentrating or limiting the region in which heat is transferred to thefluid. It has been found by experience that in many cases this furtherimproves the frequency response of the probe.

I claim:

1. In measuring apparatus for measuring a condition a metallic bodyhaving an opening at one end,

a thin walled metallic closure for said opening having an outer faceexposed to the fluid, and

a temperature sensitive electrical element engaged within the inner faceof said closure,

said temperature sensitive element being held in engagement with saidinner face by an electrical and heat conductive adhesive cement.

2. In measuring apparatus for measuring a condition a metallic bodyhaving an opening at one end,

a thin walled resilient metallic closure disc for said opening having anouter face exposed to the fluid, and

a temperature sensitive electrical element engaged with the inner faceof said closure,

said disc providing a resilient force for maintaining contact betweensaid disc and said element.

3. In measuring apparatus for measuring a condition tween the fluid andsaid element.

* i i t

1. In measuring apparatus for measuring a condition in a fluid, ametallic body having an opening at one end, a thin walled metallicclosure for said opening having an outer face exposed to the fluid, anda temperature sensitive electrical element engaged within the inner faceof said closure, said temperature sensitive element being held inengagement with said inner face by an electrical and heat conductiveadhesive cement.
 2. In measuring apparatus for measuring a condition ina fluid, a metallic body having an opening at one end, a thin walledresilient metallic closure disc for said opening having an outer faceexposed to the fluid, and a temperature sensitive electrical elementengaged with the inner face of said closure, said disc providing aresilient force for maintaining contact between said disc and saidelement.
 3. In measuring apparatus for measuring a condition in a fluid,a metallic body having an opening at one end, a thin walled metallicclosure for said opening having an outer face exposed to the fluid, anda temperature sensitive electrical element engaged with the inner faceof said closure, said closure having a thermal insulating coating on theouter face provided with a window facing said element for heat transferthrough the window between the fluid and said element.